The present invention relates to a servo track writer capable of recording servo data accurately, a magnetic disk drive, and a manufacturing method for magnetic disk drives.
The devices that use various forms of media, such as an optical disk and a magnetic tape, are known as data storage devices. Among these devices, hard-disk drives (HDDs) are most commonly used as the storage devices of computers, and the HDDs are one type of storage device indispensable in current computer systems. Additionally, the excellent characteristics of the HDDs are increasingly expanding their applications not only in computers, but also as the removable memories and similar devices used in dynamic-image recording/reproducing devices, car navigation systems, digital cameras, or the like.
The magnetic disks used in an HDD each have a plurality of concentrically formed tracks, and each track has a data region into which user data will be stored, and a servo region into which address information (servo data) will be stored. The magnetic head formed of a thin-film element can read or write data by accessing a desired region (address) in accordance with address information.
A cylinder ID, a servo sector number, a burst pattern, and the like are stored as servo data in the servo region. Track IDs identify the addresses of tracks, and servo sector IDs identify the addresses of servo sectors. The burst pattern contains information on the relative positions of the magnetic head with respect to tracks. The burst pattern that is an array of regions formed at fixed intervals in the radial direction of the disk, each region having signals stored therein, is constituted by multiple banks of signal storage regions different from one another in terms of phase.
Data is read out from or written onto the magnetic disk while the position of the magnetic head is being confirmed against servo data in a rotating condition of the magnetic disk. Servo data that has been read by the magnetic head undergoes arithmetic processing by a controller. The value of the electric current to be supplied to a voice coil motor (VCM) is determined from the relationship between the current position and desired position of the magnetic head. The controller generates control data (DACOUT) that indicates the above-calculated electric current value, and supplies the data to a VCM driver. If a shift in position occurs, the controller drives a carriage so as to compensate for the shift, and conducts position control of the magnetic head.
HDDs tend to have a narrower track spacing for higher track density in order to meet the recent needs of higher capacity. To obtain narrower tracks, the above-mentioned servo data for controlling the positioning of the head needs to be recorded more precisely, and in this sense, the servo track write (STW) process for writing the servo data becomes a very important production process. Efforts are therefore being made to improve positioning accuracy by, for example, using the encoder of a more accurate optical system or recording only the disk in an external STW process. However, the improvement has not yet been achieved since air disturbance due to disk rotation or the fluttering of the disk itself becomes the governing factor in the accuracy of the servo track write operation.
Patent Document 1 (U.S. Patent Application Publication No. 2003/0081344) discloses a servo track writer that performs the servo track write operation in a room placed under a low-density gas atmosphere. In the technology described in Patent Document 1, STW is executed by inserting into a servo track writer the disk drive into which servo data is to be written, and substituting a low-density gas (such as a helium gas) for the internal atmosphere of a room in which the servo track writer is to be placed. Vibration of the disk in the STW process is reduced by executing STW in the low-density gas atmosphere.
In the servo track writer described in above Patent Document 1, however, since a helium gas is used in STW, manufacturing processes become complex and troublesome and manufacturing costs increase. It is desirable to improve servo track write accuracy by reducing disk vibration in the STW process without substituting the disk drive interior by a gas different from air, such as a helium gas.